Precipitation Amount: but only when very tall (congestus)


If you’ve never spotted a Cumulus cloud, then you need to get out more. This has to be one of the easiest types to add to your cloud collection (which explains why it only earns one star). Cumulus clouds are the cotton-wool puffs, with flat bases, that drift lazily across the sky on a sunny day. Generally forming a few hours after daybreak, they tend to dissipate before sundown, for they form on thermals – invisible columns of air rising from the ground as it is warmed by the sun.

Most forms of Cumulus produce no rain or snow, and so are known as fair-weather clouds. But in unstable air, their bright, crisp cauliflower mounds can build upwards so that they develop from the small humilis species, through mediocris to the largest form, Cumulus congestus. With its ominous, shadowy base, this cloud is no longer fair-weather. Congestus can produce brief but sizeable showers, and can keep growing into fierce Cumulonimbus storm clouds.

The little ones, by contrast, are scary only when they take the form of David Hasselhoff.